Nanocrystalline alloy improves PRAM

PORTLAND, Ore.—Phase-change memory (PCM) technology could profit from a new material that improves performance over traditional materials with binary eutectic-alloy nanostructures (BEANs). Researchers at the Lawrence Berkeley National Laboratory and the University of California-Berkeley claim that BEANs can be formed into high density arrays of nanowires or quantum dots whose state can be switched from amorphous to crystalline in nanoseconds.

Traditional PCM materials use chalcogenide glass materials that can be switched crystalline and amorphous states—representing a "1" or "0"—with the application of heat. BEANs works similarly, but is made from an alloy of metal and semiconductor that melts and solidifies at a temperature which is lower than the melting points of a single material.

Experimentally, the researchers led by UC Berkeley professor Daryl Chrzan, combined a germanium semiconductor with metallic tin embedded in silicon dioxide, demonstrating rapid cooling to stabilize the amorphous phase as well as the ability to tune the phase-changing material transformation into the crystalline or "bilobed" phase. Both states of the half metallic and half semiconductor material were shown to be stable at room temperature for long-term retention in PRAMs.

The researchers are currently characterizing the durability of the material after repeated switching between "1" and "0" as well as performing further optimization of the switching process.

Diagram shows enthalpy curves sketched for the liquid, crystalline and amorphous phases of a new class of nanomaterials called “BEANs” for Binary Eutectic-Alloy Nanostructures. Image credit: Daryl Chrzan